STR3A151D

Duty Cycle:	74%
Mounting Type:	Through Hole
Supplier Device Package:	8-DIP
Package / Case:	8-DIP (0.300", 7.62mm)
Operating Temperature:	-40°C ~ 115°C (TA)
Control Features:	--
Fault Protection:	Current Limiting, Over Load, Over Temperature, Over Voltage
Power (Watts):	37W
Frequency - Switching:	67kHz
Series:	STR3A100
Voltage - Supply (Vcc/Vdd):	8.1 V ~ 32 V
Voltage - Start Up:	15.3V
Topology:	Flyback
Voltage - Breakdown:	650V
Internal Switch(s):	Yes
Output Isolation:	Isolated
Part Status:	Active
Packaging:	Tube

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STR3A151D Application Field and Working Principle

The PMIC - AC DC Converters, Offline Switchers includes products from different makers with various outputs, input voltages and many more parameters. A typical example of this category is the STR3A151D by ST Micro a ZCS-NMOS(Zero Current Switching non-overlapping MOSFET Driver) offline Switcher.

STR3A151D: Introduction

The STR3A151D is an offline Switcher functioning as a primary side controller for flyback converter. Its architecture offers a wide range of protection like OVP (Overvoltage protection), OCP ( Overcurrent protection) and UVP (undervoltage Protection).This IC also contains a power-on latch, open HV pin detection, a temperature protection circuit and a dead time setting circuit.

Applications

The STR3A151D has a wide range of applications such as AC/DC adapters and power supplies, LED drivers and electronic ballast, solar and wind inverters, LED street lights, consumer-applications and home appliances.

working principle

The STR3A151D works based on the Zero Current Switching (ZCS) topology. It is a sophisticated control algorithm where the MOSFET triggering is performed by controlling the drive current in order to limit the switching losses. The ZCS technology is based on early blanking of the drive current when the voltage of the power source connected to the primary switch of the flyback converter exceeds a certain level. This technique is used to reduce the switching losses and to optimize the efficiency of the power supply.In ZCS operation, the IC includes an Internal Current sense which measures the current through the MOSFET. When the threshold of the current sense is crossed, the IC will turn off the MOSFET drive. This allows for reliable and energy efficient operation.When an input voltage is applied to the primary switch, the STR3A151D charges the storage capacitance, priming the IC for a soft-startoperation and sending a gate drive to the MOSFET. During this period the IC will continuously measure the input voltage and the output current.When the levels of measured parameters reach certain pre-programmed thresholds, the STR3A151D will turn off the drive current to the MOSFET, which disconnects the power source from the primary switch, thus completing a switching cycle.Furthermore, the onboard circuitry in the STR3A151D monitors the input and output voltages, the output current and the temperature, in order to perform various protection functions.

Power Loss Calculation

The Macro Model (MM) technique is used to calculate the power loss. It is based on simplifying the main components of the switching circuit, such as the MOSFET and the inductor, in order to obtain reliable estimations on power losses.The MM technique bases its calculations on the component datasheets, and it is composed of two main terms: 1. The power dissipated in the switching MOSFET: this term takes into account the junction-to-case thermal resistance of the component and the power losses of the MOSFET2. The power dissipated in the flyback inductor. This term considers the leakage inductance and the core losses of the component.Finally, the Macro Model technique will forecast the total power losses of the switching stage.

Conclusion

The STR3A151D is a very versatile IC designed for use in a wide range of applications. Its sophisticated Zero Current Switching control algorithm, combined with an efficient power loss calculation technique, make it an ideal choice for low power and high efficiency designs. Its integrated protection circuits guarantee reliable operational and prevention of component failure caused by overvoltage, overheat and over current conditions.The STR3A151D is a cost-effective solution and is widely used in a variety of applications such as AC/DC adapters and power supplies, LED drivers and electronic ballast, solar and wind inverters, LED street lights, consumer-applications and home appliances.

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